Radio-frequency transformer



Dec. 23, 1947. J. E. TILLMAN RADIO FREQUINCY TRANSFORHER Filed July 21, 1945 Figi.

Inventor: John E. Tillr'rah3 lbg /VmM/ Jud/w14 HS Attorheg.

Patented Dec. 23, 1947 RADIO-FREQUENCY TRANSFORMER John E. Tillman, Stratford, Conn., assigner to General Electric Company, a corporation of New York Application July 21, 194,3, Serial No. 495,657` 12 claims. (C1. 1v1-vri) 1 My invention relates to radio receiving apparatus and in particular to means for coupling the high frequency circuits of such apparatus.

In the manufacture of radio frequency transformers for use in the radio frequency and intermediate frequency stages of radio receivers, it is desirable to employ, in so far as possible,

identical component parts for different sizes of y transformers, the desired variations in inductance and quality being secured by the use of different windings. Furthermore, it is desirable to use small units for the magnetic structures of the transformers which are quickly and easily assembled. It is well known to use suitably molded powdered iron magnetic cores and pole pieces in such transformer arrangements because of the ease of thus forming small magnetic bodies and tuning cores having desirable magnetic properties. Accordingly, it is an object of my invention to provide an improved radio frequency transformer which comprises a plurality of identical and interchangeable parts and which is quickly and easily assembled.

It is another object of my invention to provide.

an improved coupling arrangement for a radio frequency transformer.

Still another object of my invention is to provide an improved link coupling for the windings of a radio frequency transformer in which the degree of coupling may be varied with facility and precision.

It is a further object of my invention to provide an improved radio frequency transformer in which the inductance of the individual windings may be varied over a broad range of values without an appreciable alteration of the quality of the winding.

A still further object of my invention is to provide an improved link coupling for controlling the mutual inductance of the windings of a radio frequency transformer in which the mutual inductance may be switched alternately from a maximum adjusted value to a minimum adjusted value to provide both broad and sharp selectivity positions of a receiver circuit under different operating conditions.

Still another object of my invention is to provide an improved high frequency transformer which is substantially completely shielded from adjacent receiver, circuits.

One of the features of my invention comprises the enclosing of the magnetic structures of a high frequency transformer in a non-magnetic conductive housing which functions to link the component windings of the transformer and of- 2 varying the degree oi said linkage in adjustable increments.

Another feature of my invention comprises the utilization of iixed and movable tuning cores for adjusting the self-inductance of a high frequency inductance, the movable core being constructed and arranged to maintain a substantially constant value of Q for the coil over a broad range of values of inductance.

Thefeatures of my invention which I believe to be novel are set forth with particularty in the appended claims. My invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing, in which Fig. 1 is a side elevation View, partly in section, of a transformer embodying my invention; Fig. 2 is a plan View of a portion of the transformer of Fig. 1 along the line 2 2; and Fig. 3 is a modification of one of the elements employed in the arrangement of Fig. 1.

Referring to Figs. l and 2 jointly, I have shown a radio frequency transformer which comprises a hollow main body member ID formed of a conductive non-magnetic material, such as aluminum or copper, and which is constricted at its center to form two cylindrical recesses II and I2 in which are disposed the magnetic elements and the windings of the transformer. For purposes of production and ease of assembly, the magnetic structures disposed within each of the recesses II and I2 are of identical construction.

The magnetic construction of the primary, or left-hand, side of the transformer arrangement comprises a pair of circular cup-shaped members I3, I4, positioned with their open sides in opposed relation to form a substantially closed magnetic body member and formed preferably by molding or compressing and machining powdered iron particles. Each of the cup-shaped members I3, III has a central aperture I5 which is provided with a shoulder portion I6 for the reception of the opposite ends of a tubular form I'I of arsuitable dielectric material, upon which is wound the transformer winding I8.

A fixed tuning core 2D, constructed of powdered iron particles, is supported by the upper magnetic member I3, being secured thereto in any desired fashion. The fixed core 20 extends downwardly into the tubular form I'I a distance which is determined by the amount of variation of the selfinductance desired for the winding I8.

A 'movable tuning core 2I, having a length core 20 to the bottom of the opening I5 in magnetic member I4, is supported by means of stud 22 in threaded engagement with suitable threads in the bottom wall of member I0. The stud 22 preferably is formed of a non-magnetic material, such as brass, in order to provide a desired operating characteristic for winding I8 in a manner to be pointed out later. A slot 23 at the lower end of stud 22 provides means for adjusting the position of tuning core 2| with respect to the member I4 and the fixed core 20.

In order to permit the desired amount of variation in self-inductance of winding I8, the magnetic member I4 is supported by a shoulder 24 on the internal surface of opening II and spaced from the bottom of this opening a distance equal to the length of the movable tuning core 2|.

The right-hand, or secondary, winding of the transformer arrangement depicted in Fig. 1 is of identical construction with that discussed in conjunction with the left-hand portion of the transformer.

Therion-magnetic body member I is likewise provided, on its inner surface near its upper end, with a recess 25 for supporting a terminal board 26 of any suitable dielectric material and upon which is mounted a plurality of contact elements 21 to which the windings I8 are electrically ccnnected by means of leads 23, A pair of threaded studs 29, in threaded engagement with tapped holes provided in body member I0, function both as means to secure the terminal board 26 to the transformer arrangement and to support the transformer arrangement as a unit from any suitable supporting structure, such as a radio chassis.

Since the primary and secondary windings of the transformer arrangement thus far described are substantially magnetically isolated from one another by the center wall 3| of the non-magnetic body member IIl, the sole coupling between the primary winding |8 and the secondary winding I8' is through the link coupling provided by the body member III. This housing I0 acts as a one turn link in which currents are induced by the magnetic field set up by the primary currents flowing in the winding I8 and linking the left-hand portion of the body member I0. In order to provide means to permit the currents induced in the left-hand portion of body member I0 to link the magnetic structure and the Winding of the secondary coil I 8', the central wall 3| of body member I0 is provided with a narrow slot 32, better indicated in Fig. 2, which may be an air gap or may be a path filled with any other suitable dielectric material and which extends between the recesses II and I2. Also, a tapped hole 33 extends from the top to the bottom of body member IU at the center of slot 32. A screw 34, in threaded engagement with the threaded hole 33 and provided with a slot 35 at its lower end for adjusting its position within the threaded hole 33, functions as means for short-circuiting an adjustable length of slot 32 to vary the amount of link coupling between the primary and secondary windings.

In adjusting the self-inductances of the windings of the transformer arrangement described, as well as the mutual inductance of these windings for operation in a given receiver circuit, the movable tuning slugs. or cores, 2| are adjusted by means of the studs 22 to obtain lthe desired value of self-inductance of each of the primary and secondary windings. Because 0f the presence of the non-magnetic stud 22 inserted in the core 2|, the losses of the core are not uniform along the axis of winding I 3 and the Q of the respective circuit varies in a determinable manner as adjustment of the self-inductance is made. Thus, when the movable core 2| is lowered and the gap between the cores and 2| enlarged, the portion of the movable core 2| which includes the non-magnetic stud 22 emerges from the hole I5 and the Q of the coil tends to rise due .to remoyal of the stud and its associated losses. At the same time the core is being removed and the Q of the coil tends to drop due to decrease in inductance. Thus, this particular form of :tuning core gives a region of adjustment where the quality of the transformer circuits and the overall gain of the transformer are substantially constant as the individual windings of the transformer are tuned by adjustment of the movable tuning core 2|.

After the self-inductances of the individual windings have been adjusted to desired values, the mutual inductance is adjusted by varying thc position of screw 34 In the tapped hole 33. When screw 34 is at the bottom of the tapped hole 33, the primary and secondary windings of the transformer are greatly overcoupled duc to the large cross section of the single turn loop coupling these windings. As the screw 34 is moved upwardly in the tapped hole 33, however, an increasingly larger portion of the link coupling is shcrt-circuited between the coils until, when the screw 34 is almost entirely within the transformer housing member, very loose coupling of the windings is obtained. Thus, the short-circuiting element 34 provides means by which the degree of link coupling and the mutual inductance of the primary and secondary windings of the transformer may be easily and quickly adjusted to a precise value.

In Fig. 3, I have shown a modification of the short-circuiting screw used in the tapped hole 33 for adjusting the mutual inductance of the windings. The screw 39 shown in this figure is provided with a longitudinal slot 40 and is used in conjunction with another screw 4| inserted in the opposite end of tapped hole 33. When this mutual inductance adjusting screw is used in the tapped hole 33 and the position of the screw is arranged so that slot 40 is parallel with the slot 32 in the non-magnetic housing II), a maximum amount of the coupling is provided for all depths of the screw in hole 33. This maximum amount may be adjusted by screw 4I. However, when the screw 38 is turned through 90o so that the slot 40 is transverse to slot 32, a minimum amount of coupling is secured, the exact amount being determined by the depth of the screw 39 in the tapped hole 33. Such an arrangement of the coupling screw is especially useful when the tuning of the receiver circuits is being adjusted with the aid of a cathode ray tube. By merely rotating the screw 39 through 90, the transformer characteristic at maximum coupling may be compared with that at the coupling for the particular setting of the coupling screw. As an alternative structure, of course, the slot 40 may be filled with a dielectric material. Also, when a desired adjustment of mutual inductance has been made, a lock nut 42 may be employed for maintaining the screw 33 in its adjusted position. When it is desired to pro'vide both broad and sharp selectivity positions .on a receiver, the lock nut is omitted and the screw 39 is mechanically operated from a control at the front of the receiver. It is thus seen that the transformer structure described above is one particularly adapted for rapid production in large quantity. 'I'he magnetic cores I3 and I4 may be employed with any de- -sired sizes of windings. Likewise, the non-mag-v netic housing Ill is one which permits thev use of circular magnetic cores having the same outside diameter, but having any desired thickness of walls to give a particular characteristic. The par ticular -self-inductance adjusting arrangement disclosed is one which provides easy and accurate tuning of the individual cores, while the means and method of adjusting the mutual inductance of the transformer windings are well adapted to provide 4the desired degree of exibility of adjustment required to compensate for the nonuniformities which occur in mass production of transformers of this type due to variations in molding of the magnetic bodies and thickness of the walls of the various elements. The arrangement, moreover, provides means for adjust ing easily and rapidly to a desired amount of coupling of the individual windings.

While I have shown a particular embodiment of my invention, it will, of course, be understood that I do not wish to be limited thereto since various modifications may be made, and I contemplate by the appended claims to cover any such modications as fall within the true spiritv an-d scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. The combination, in a radio frequency transformer, of a body member of conductive non-magnetic material having a plurality of recesses therein', said recesses being separated by a wall of said body member, each of said recesses having a corresponding winding of said transformer positioned therein and said body member forming a link coupling between said windings, said wall having a dielectric path extend ing between said recesses, and means for adjusting the dimensions of said path to vary the degree of said coupling and the mutual inductance of said windings.

2. The combination, in a radio frequency transformer, of a body member of conductive nonmagnetic material having a plurality of recesses therein, said recesses being separated by a wall of said body member, each of said recesses having a corresponding winding of said transformer and a cooperating magnetic structure positioned therein and said body member forming a link coupling between said windings, said wall having a dielectric path extending between said recesses, and means for adjusting the dimensions of said path to vary the degree of said coupling and the mutual inductance of said windings.

3. The combination, in a radio frequency transformer, of a body member of conductive non-magnetic material having a plurality of recesses therein, said recesses being separated by a Wall of said body member, each of said recesses having a corresponding winding of said transformer and a cooperating magnetic structure positioned therein and said body member forming a link coupling between said windings.

means for adjusting the self-inductances of saidA windings, said wall having an air gap extending between said recesses, and means for adjusting the dimensions of said gap to vary the degree of said coupling and the mutual inductance of said windings.

4. A radio frequency transformer comprising a body member of conductive, non-magnetic material having a pair of recesses therein, said recesses being connected by a narrow slot through a wall of said body member, each of said recesses having a corresponding winding of said transformer positioned therein and said body member forming a current carrying loop inductively coupled with said windings, and means for varying the length of said slot to adjust said coupling and the mutual inductance of said windings.

5. lA radio frequency transformer comprising a body member of conductive, non-magnetic material having a recess therein, a pair of windings positioned within said recess in spaced relation, said recess being constricted between said windings substantially to isolate each of said windings from the magnetic eld of the other of said windings and said body member forming a current carrying loop inductively coupled with said windings, and means for short-circuiting said loop at a point between said windings.

6. A radior frequency transformer comprising a body member of conductive, non-magnetic material having a pair of recesses therein, said recesses being connected by a narrow slot through a wall of said body member, each of said recesses having a corresponding Winding of said transformer positioned therein and said body member forming a current carrying loop inductively coupled with said windings, and means for shortcircuiting an adjustable portion 'of said slot to adjust said coupling and the mutual inductance of said windings.

7. A radio frequency transformer comprising a body member of conductive, non-magnetic material having a recess therein, a pair of windings positioned within said recess in spaced relation, said recess being constricted between said windings substantially to isolate each of said windings.

from the magnetic eld of the other of said windings and said body member forming a current carrying loop inductively coupled with said windings, and means for short-circuiting said loop at an adjustable point between said windings.

8. A high frequency inductance unit comprising a substantially closed magnetic body member having a centrally disposed inwardly directed magnetic core member extending from an inner wall of said body member a portion of the way toward the opposite inner wall of said body member, a winding positioned within said body member and encircling said core member, said body member having an opening in said opposite wall,

and a movable magnetic member extending through said opening toward said core member, the magnetic losses of said movable member varying gradually along its length whereby as said member is moved through saidopening to vary its distance from said core member and the in vductance of said winding the quality of said winding is maintained substantially constant over a wide range of inductance.

9. A radio` frequency transformer comprising a body member of conductive, non-magnetic material. having a pair'of recesses therein, said recesses being connected by a narrow slot through a wall of said body member, each of said recesses having a corresponding winding of said transformer positioned therein, said body member forming a current carrying loop inductively coupled with said windings, and a slotted movable conductor extending into one end of said slot and supported for'rotation and axial motion therethrough, whereby alignmentof the slots in said conductor and said vbody member gives a condition of maximum coupling of said windings and perpendicularity of said slots gives a condition of minimum coupling.

l0. A radio frequency transformer comprising a body member of conductive, non-magnetic material, having a pair of recesses therein. said recesses being connected by a narrow slot through a wall of said body member, each of said recesses having a corresponding winding of said transformer positioned therein, said body member forming a current carrying loop inductively coupled with said windings, a slotted movable conductor extending into one end of said slot and supported for rotation and axial motion therethrough, whereby alignment of the slots in said conductor and said body member gives a condition of maximum coupling and perpendicularity of said slots gives a condition of minimum coupling of said windings, and means to short-circuit a portion of said slot in said body member to predetermine the maximum coupling of said transformer windings.

l1. A radio frequency transformer comprising a body member of conductive, non-magnetic material, having a pair of recesses therein, said recesses being connected by a narrow slot through a wal1 of said body member, each of said recesses having a corresponding winding of said transformer positioned therein, said body member forming a current carrying loop inductively coupled with said windings, a slotted movable conductor extending into one end of said slot and supported for rotation and axial motion therethrough, whereby alignment of the slots in said conductor and said body member gives a condition of maximum coupling and perpendicularity of said slots gives a condition of minimum coupling, and means to short-circuit a. portion of said slot in said body member to predetermine the maximum coupling of said transformer windings, said means comprising a second movable conductor coaxially aligned with said slotted conductor and extending into the opposite end of said slot in said body member.

12. A high frequency inductance unit comprising a winding positioned Within a substantially closed magnetic body member, said body member having an opening in a wall thereof along the axis of said winding, and a movable magnetic tuning core extending through said opening along said axis, said movable magnetic core being mounted on and surrounding a portion of a conducting non-rnagnetic screw of such dimensions that as said core is moved along said axis to tune said winding the inductance and magnetic losses of said movable core and said screw are combined to maintain the quality of said winding substantially constant over a wide range of tuning.

JOHN E. TILLMAN.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,364,291 Harvey Dec. 5, 1944 2,130,815 Riepka Sept. 20, 1938 2,141,254 Schaper Dec. 27, 1938 FOREIGN PATENTS Number Country Date 507,655 Great Britain Sept. 15, 1937 

